Thanks for the tutorial! But why havent you just compiled pure-ftpd from the debian src package, so that you can install it with apt? We explained that in the FAQ and I use this on all of my servers.
In my opinion you replaced a small problem (compiling pure-ftpd once) with a bigger one, because now you cant install any ispconfig updates in future in your setup.
So I can only recommend to not try the above when you want to be able to install ispconfig updates in future. Not installing ISPConfig updates can be a security risk.